Retarders are hydrodynamic brakes that utilize relative rotation of the components within the retarder to assist in slowing the vehicle in which the retarder is employed. Retarders are sometimes located in association with the output of the transmission and sometimes they are located in conjunction with the input to the transmission. Both locations have relative advantages and disadvantages, as is well known to this art. The present invention, however, is directed to the control by which the retarder is actuated, or deactuated, and a control embodying the concepts of the present invention is not dependent upon the relationship of the retarder to the transmission input or output.
Retarders have historically been employed in large vehicles to assist in vehicle braking, or deceleration, particularly for the descent of steep hills in order to relieve the vehicle brakes from extended usage. The original retarders, or as they were then known, grade-retarding devices, were activated by moving the drive range selector lever to a "grade retarder range." In this position of the selector lever all drive clutches were released, and to the surprise of the uninitiated driver, the grade retarder position of the selector lever would not afford any forward drive to the vehicle. It was truly a retard-only position.
Over the years the application and control of the retarder became quite sophisticated. The current state of the art for retarder controls is depicted in FIG. 1 to provide for an on/off operation of the retarder. The retarder itself typically constitutes a bladed rotor wheel that is attached to the transmission, and a bladed stator that is fixedly positioned. In the vehicular art when a component is thus fixedly positioned it is said to be "grounded," or "fixed to ground." The rotor and the stator form a toroidal working chamber that is filled with hydraulic fluid to effect the hydrodynamic braking action, and from which the hydraulic fluid is emptied in order to deactuate the retarder.
The prior an retarder control system, designated generally by the numeral 10 in FIG. 1, requires multiple valves to satisfy all the current requirements for such devices. For example, line pressure is supplied from a pump 11 through a conduit 12 to a regulating valve 13 that is operated by the control pressure supplied by a modulating control valve 14 through a conduit 15 to the regulating valve 13. When the control pressure in conduit 15 is sufficient to open the regulating valve 13, line pressure is transferred through a conduit 16 to a signal valve 17. The signal valve 17 operates a flow control valve 18 to permit the passage of hydraulic fluid pressure through conduit 19 to the input port 20 of the retarder 21.
Hydraulic fluid exits the retarder 21 through a discharge port 22 into a conduit 23--which contains a temperature sensor 24--to be directed through the flow control valve 18 and into the intake port 25 of a cooler 26. The cooled hydraulic fluid leaves the cooler 26 through the discharge port 27 and is directed, through conduit 28, into the flow control valve 18 and thence into the feed conduit 19 that connects to the input port 20 of the retarder 21. Retarder operation does not require the continuous introduction of hydraulic fluid. Instead, the fluid within the retarder 21 is continuously worked between the rotating impeller and the fixed stator to dissipate the energy reflected by the rotating impeller to ground through the stator, and thus assist in slowing the vehicle. Although fluid flow through the retarder 21 is not necessary to its operation, the prior an systems generally do assure that a sufficient quantity of hydraulic fluid is available to the retarder 21 by virtue of a supplemental supply line 19.sub.A connected between the regulator 13 and the flow control valve 18.
Any hydraulic fluid which leaves the converter, not shown, enters the flow control valve 18 through conduit 36, and supplements the flow of lubricating fluid through the lubrication fluid distribution system feed line 38.
An air actuated accumulator 30 is provided to satisfy the initial demand for the volume of hydraulic fluid required to fill the retarder. The accumulator is connected to the intake port 25 of the cooler 26 through conduit 39.
When the retarder 21 is not needed, the modulating solenoid 14 reduces the pressure fed through conduit 15 to the regulating valve 13. When the modulating solenoid thus reduces the pressure to the regulating valve 13 continued communication of the pressurized hydraulic fluid through line 16 to the signal valve 17 is precluded, thus permitting the biasing action of the spring 31 to translate the spool valve member 32 within the flow control valve 18 such that conduit 19, which supplies hydraulic fluid to the retarder 21, is closed. Simultaneously therewith, the conduit 23 that communicates with the discharge port 22 of the retarder 21 opens through the flow control valve 18 to the hydraulic return system 33. This same translation of the spool valve member 32 also connects the return conduit 36 from the converter to the intake port 25 of the cooler 26.
A restricted flow of hydraulic fluid, which serves to lubricate and cool the retarder 21, is fed from the cooler 26, through the flow control valve 18 and through a by-pass conduit 34 that incorporates a constriction 35 to minimize the flow of hydraulic fluid therethrough.
As should now be apparent, even the most sophisticated prior art control 10 was a complicated arrangement that required several valve members to effect the desired results.